Spinal fixation devices and systems are used to align and/or fix a desired relationship between adjacent vertebral bodies. Such devices typically include a spinal fixation element, such as a relatively rigid fixation rod or plate, that is coupled to adjacent vertebrae by attaching the element to various anchoring devices, such as hooks, bolts, wires, or screws. The fixation element can have a predetermined contour that has been designed according to the properties of the target implantation site, and once installed, the fixation element can hold the vertebrae in a desired spatial relationship, either until desired healing or spinal fusion has taken place, or for some longer period of time.
In use, a spinal fixation element can be anchored to specific portions of a vertebra. Since each vertebra varies in shape and size, a variety of anchoring devices have been developed to facilitate engagement of a particular portion of the bone. Pedicle screw assemblies, for example, have a shape and size that is configured to engage pedicle bone. Such screw assemblies typically include a threaded shank capable of being positioned within a vertebra, and a head portion having a fixation rod-receiving element, usually in the form of a U-shaped recess. A set-screw, plug, or similar type of closure mechanism can be used to secure the fixation element, e.g., a spinal rod, into the rod-receiving head of the pedicle screw.
Often, such fixation procedures will require some degree of manipulation of the spinal construct(s) in order to properly position the fixation element and/or to achieve the desired therapeutic effect. Typically, such manipulation includes compression or distraction of the construct. However, these manipulation steps can be problematic as the working area tends to be crowded and the required instrumentation can be difficult to position, adjust, and/or maintain at a desired location.